The IRS provides a centralized unit for mailing your Form 8857 (Request for Innocent Spouse Relief). The mailing address you are to directly send your completed form (along with explanation statement) to is:
IRS - IRS-Stop 840-F
PO Box 120053
Covington, KY 41012
Be certain you send your request for innocent spouse relief form to this address, and not your usual IRS tax return address. By sending your request to any other address, of course, the processing time will lengthen.